Electric heater for heating a selected portion of workpiece and method of heating the workpiece by the heater

Abstract

An electric heater for heating a workpiece including at least one heat generating wire which generates heat upon application of an electric current thereto, and which has a diameter of not more than 1 mm. Each heat generating wire has a heating portion which is formed by bending so as to at least partially define a heating space. The workpiece to be heated by the electric heater is positioned relative to the heating space, such that the workpiece is spaced apart from the heating portion of the heat generating wire or wires.

What is claimed is: 
     
       1. An electric heater for heating a glass coating on a resistor body of a resistor thereby forming a protective glass covering, said resistor having first and second lead wires, each of which is connected to respective opposite ends of said resistor body, the electric heater comprising: at least one heat generating wire which generates heat upon application of an electric current thereto, each of said at least one heat generating wire having a bent heating portion whose shape at least partially defines a heating space, said heating portion having a length which is smaller than a length of said glass coating so that only said glass coating, except end portions thereof, is accommodated in said heating space, said heating portion being further dimensioned so that said glass coating is spaced apart from said at least one heat generating wire;   a pair of terminal portions connected to opposite ends of said heating portion, for connecting said heating portion to an external power source; and   first and second heat radiating members contacting said first and second lead wires, respectively, so that heat transferred to said first and second lead wires from said glass coating and said resistor body is radiated through said first and second heat radiating members.   
     
     
       2. An electric heater according to claim 1, wherein said heating portion of said each heat generating wire takes the form of a cylindrical coil having a plurality of cylindrical turns, said glass coating of said resistor body being positioned in a cylindrical space defined by said cylindrical coil. 
     
     
       3. An electric heater according to claim 1, wherein said heating portion of said each heat generating wire takes the form of a rectangular coil having a plurality of rectangular turns, said glass coating of said resistor body being positioned in a rectangular space defined by said rectangular coil. 
     
     
       4. An electric heater according to claim 1, wherein said at least one heat generating wire consists of two heat generating wires, said heating portions of one of said two heat generating wires cooperating with said heating portion of the other heat generating wire to define said heating spaced therebetween. 
     
     
       5. An electric heating according to claim 4, wherein said heating portions of said two heat generating wires are movable toward and away from each other. 
     
     
       6. The electric heater of claim 1, wherein each of said at least one heat generating wire has a diameter of not more than 1 mm. 
     
     
       7. The electric heater of claim 1, wherein said first and second heat radiating members consist of a pair of insulative tubes which are disposed adjacent said pair of lead wires and extend along an axial direction of said resistor body. 
     
     
       8. The electric heater of claim 1, wherein said pair of lead wires is formed of a base metal. 
     
     
       9. An electric heater for heating a glass coating on a resistor body of a resistor thereby forming a protective glass covering, said resistor having first and second lead wires, each of which is connected to respective opposite ends of said resistor body, comprising: at least one heat generating wire which generates heat upon application of an electric current thereto, said heat generating wire having a bent heating portion whose shape at least partially defines a heating space, at least said glass coating being accommodated in said heating space without contacting said heat generating wire, so that said glass coating is fired by said heating portion; and   first and second adiabatic members disposed adjacent said heat generating wire and around said first and second lead wires, respectively, such that said first and second lead wires are substantially completely insulated from the heat generated by said heating portion.   
     
     
       10. The electric heater of claim 9, wherein said heating portion fires said first portion at temperatures ranging from 500°-800° C. 
     
     
       11. The electric heater of claim 9, wherein said adiabatic member consists of an insulative tube which is disposed completely around said second portion and extends along an axial direction of said resistor body. 
     
     
       12. The electric heater of claim 9, wherein said heat generating wire has a diameter of not more than 1 mm. 
     
     
       13. The electric heater of claim 9, wherein said pair of lead wires are formed of a base metal. 
     
     
       14. A method of heating a glass coating on a resistor body of a resistor thereby forming a protective glass covering, said resistor having first and second lead wires, each of which is connected to respective opposite ends of said resistor body, the method comprising the steps of: forming at least one heat generating wire which generates heat upon application of an electric current thereto, so that said heat generating wire has a bent heating portion whose shape at least partially defines a heating space, and so that said heating portion has a length which is smaller than a length of said glass coating;   forming a pair of terminal portions at opposite ends of said heating portion for connecting said heating portion to an external power source;   forming a pair of heat radiating members near said heating portion;   positioning said resistor relative to said heating space such that said glass coating is spaced apart from said heat generating wire, only said glass coating except for end portions thereof is accommodated in said heating space and said pair of lead wires are supported by said heat radiating members;   applying an electric current to said heat generating wire such that only said glass coating is fired by said heating portion, and such that heat transferred to said lead wires from said glass coating and said resistor body is radiated through said heat radiating members; and   removing said resistor from said heating space.   
     
     
       15. The electric heater of claim 14, wherein said pair of lead wires are formed of a base metal. 
     
     
       16. A method of heating a glass coating on a resistor body of a resistor thereby forming a protective glass covering, said resistor having a pair of lead wires, each of which is connected to respective opposite ends of said resistor body, comprising the steps of: forming at least one heat generating wire which generates heat upon application of an electric current thereto, so that said heat generating wire has a bent heating portion whose shape at least partially defines a heating space;   forming a pair of adiabatic members near said heating portion;   positioning said resistor relative to said heating space such that said glass coating is spaced apart from said heat generating wire and said pair of lead wires are disposed within said adiabatic members;   applying an electric current to said heat generating wire such that said adiabatic members substantially completely insulate said lead wires from heat generated by said heating portion; and   removing said resistor from said heating space.   
     
     
       17. The electric heating of claim 16, wherein said pair of lead wires are formed of a base metal.